The present invention relates to a method of forming a pressure-contact typ semiconductor device.
FIG. 1 is a sectional view showing a conventional pressure-contact type semiconductor device disclosed in Japanese Published Patent specification No. Sho. 46-35213.
In FIG. 1, the reference numeral 1 designates a diode element in which an anode is formed on one main surface and a cathode is formed on the other main surface. The numeral 2 designates an anode conductor, and the numeral 3 designates a cathode conductor. The anode conductor is formed of a copper post in which a recess portion 2a for containing the diode element 1 is formed at one end and a mounting bolt 2b is provided at the center of the other end, and a mounting bolt 2b is provided at the center of the other end. The anode of the diode element 1 is pressure contacted with the bottom surface of the recess portion 2a. The cathode conductor 3 is made of a copper material, and has a plate-shaped portion pressure contacted with the cathode of the diode element 1, and a cathode leading rod at the central part of the plate-shaped portion. The numeral 4 designates an insulating washer. The numeral 5 designates a metal washer. The numerals 6a, 6b and 6c designate leaf springs. The numeral 7 designates a metal cylindrical body. The numeral 8 designates projections provided at the cylindrical body 7. The projections 8 are formed to be engaged with the outer peripheral edge of the upper surface of the upper stage 6c of the leaf springs 6a, 6b and 6c of compressed state at a plurality of positions in a circumferential direction of the side wall of the cylindrical body 7. These projections 8 have a function for pressure contacting the cathode conductor 3 with the cathode of the diode element 1 by the spring pressures of the leaf springs 6a, 6b and 6c of compressed state and for pressure contacting the anode of the diode element 1 with the recess portion 2a of the anode conductor 2.
FIG. 2 is a sectional view of the essential portion for describing one method of forming a projection for engaging the leaf springs of compressed state with the side wall of the metal cylinder of the conventional example.
In FIG. 2, the same reference numerals are used to designate the same or corresponding parts or elements as those shown in FIG. 1.
The leaf springs 6a, 6b and 6c are first pressed in a compressed state by a tubular pressing jig 50. The outer diameter of the tubular body of the jig 50 is smaller than that of the leaf spring 6c as shown in FIG. 1. Further, the inner diameter of the tubular body is larger than the outer diameter of the cathode leading rod. Then, a plurality of positions (the portions corresponding to the outer peripheral edges of the leaf spring 6c) on the periphery of the side wall of the cylindrical body 7 are broken by the ends of bites 51, thereby forming the projections 8 engaged with the outer peripheral edge of the upper surface of the leaf spring 6c.
The projections 8 of the conventional example are formed as described above. Thus, if the distance (designated by h) between the lower surfaces of the bites 51 and the outer peripheral edge of the upper surface of the leaf spring 6c of the leaf springs 6a, 6b and 6c of compressed state becomes close to 0, the ends of the bites 51 damage the leaf spring 6c when the ends of the bites 51 break the side wall of the cylindrical body 7. If the distance h is increased in order to prevent the damage of the leaf spring 6c, the leaf spring 6c might not be engaged with the projections 8 when the jig 50 is removed after the projections 8 are formed. Therefore, it is not easy to form the projections 8 so that the spring pressures of the leaf springs 6a, 6b and 6c become a predetermined value.
Furthermore, when the projections 8 are formed by breaking the side wall of the cylindrical body 7 by the ends of the bites 51, small broken pieces might be generated from the forming portions of the projections 8 of the side wall of the cylindrical body 7. These broken pieces fall down on the portion between the metal washer 5 of the insulating washer 4 and the cathode leading rod of the cathode conductor 3, as exemplified by the reference character A in FIG. 2, when the leaf spring 6c is engaged with the projections 8 by removing the jig 50, and cause a short-circuit between the anode and the cathode of the diode element 1, thereby lowering the electric characteristics.